Planetary mills capable of generating large gravitational, or G, forces on powders being processed are expensive to build and difficult to balance due to their high rotational speeds. Additionally, given the heat generation created by the milling process and friction of the rotating components, cooling is required to avoid damaging critical parts when operating continuously for long periods of time as well as to maintain the powders being milled at cool temperatures. Insufficient heat transfer and heating up of the components during operation may result in damage due to expansion given the tight tolerances required for a well-balanced and operating planetary mill as well as substandard milled powders. Key components which must be cooled include, for example, the large bearings typically used to support the milling chambers.
Prior art cooling methods include a simple direct contact method wherein a cooling fluid such as water, is directed towards the components to be cooled using spray jets. The effectiveness of this method is however limited by the design of the spray jets and the effective contact surface area for heat transfer. Alternatively, the components can be internally cooled, however the design of such a cooling system is very complex due to the high rotational speeds of the components.
Additionally, given the large centrifugal forces which are brought to bear on the rotating components of the planetary mill system, the components must be re-enforced or may have a limited capacity, thereby increasing costs of the assembly and reducing the cost effectiveness of milling using the assembly.